Conventionally, uninterruptible power supply apparatuses have been widely used as power supply apparatuses for stably supplying alternating current (AC) power to an important load such as a computer system. As shown for example in Japanese Patent Laying-Open No. 07-298516 (Patent Document 1), an uninterruptible power supply apparatus generally includes a converter converting commercial AC voltage to direct current (DC) voltage, an inverter converting DC voltage to AC voltage and supplying the AC voltage to a load, and a bidirectional chopper circuit supplying the DC voltage generated by the converter to a battery when the commercial AC voltage is supplied and supplying DC voltage of the battery to the inverter when the commercial AC voltage is interrupted.    Patent Document 1: Japanese Patent Laying-Open No. 07-298516